组合查询=实体+模板方法——机房重构点滴积累

    准备敲组合查询的时候，通过上网查资料、看同学们的博客，渐渐有了思路，实践的时候，遇到了令人纠结的“DataTable”和“List（of  ）”，关于这两个知识点都各有千秋，网上也有一些介绍，但是总的来说还是用泛型比较好；下面是一些参考网址：

http://bbs.csdn.net/topics/300078386

http://www.2cto.com/kf/201208/145060.html

http://bbs.csdn.net/topics/330143216

datatable和泛型总的来说：

如果是全部内容提前的话可以用datatable

datatable消耗内存，无法直观看出字段数据类型

使用datatable需要对数据库中的表有比较熟悉的了解

datatable.rows[0][1]，返回DateTable表中第一行第二列的值

datatable比较容易写错，而且编译器不检查，不符合面向对象编程的思想

了解了这些之后具体到组合查询，组合查询用到了模板方法，将相同的代码提前到父窗体

UI层代码：

<span style="font-family:SimSun;font-size:18px;"> '第一行不能为空
        Dim i As Integer
        If GroupBox1.Controls(i).Text = "" Then
            MessageBox.Show("第一行查询条件不能为空", "温馨提示")
            Exit Sub
        End If

        '如果第一个组合条件不为空
        If cmbCombin1.Text <> "" Then
            If GroupBox1.Controls(i).Text = "" Or GroupBox2.Controls(i).Text = "" Then
                MsgBox("请完善要查询的条件", vbOK + vbExclamation, "温馨提示")
                Exit Sub
            End If
        End If
        '如果第二个组合条件不为空
        '判断同时………………

        '给实体传参
        Dim mylist As New Entity.CHECKEntity
        mylist.getTable = GetTable() '得到数据表名字
        mylist.GetEntity = GetEntity() '得到实体

        mylist.CmbName1 = GetEnglish(cmbName1.Text.Trim)
        mylist.CmbName2 = GetEnglish(cmbName2.Text.Trim)
        mylist.CmbName3 = GetEnglish(cmbName3.Text.Trim)
        '选择关系
        mylist.CmbRelation1 = cmbRelation1.Text.Trim
        mylist.CmbRelation2 = cmbRelation2.Text.Trim
        mylist.CmbRelation3 = cmbRelation3.Text.Trim
        '要查询的内容
        mylist.TxtQuery1 = txtQuery1.Text.Trim
        mylist.TxtQuery2 = txtQuery2.Text.Trim
        mylist.CmbRelation3 = txtQuery3.Text.Trim
        '组合
        mylist.CmbCombination1 = GetEnglish(cmbCombin1.Text.Trim)
        mylist.CmbCombination2 = GetEnglish(cmbCombin2.Text.Trim)
        '定义实体接信息
        Dim result As Object
        Dim facadep As New Facade.CHECKFacade
        result = facadep.QueryFacade(mylist)
        If result.count = 0 Then
            MsgBox("么有符合记录的信息", , "温馨提示")
            Exit Sub
        Else
            '把实体信息传到窗体
            Call Todgv(result)
        End If</span>

     在父窗体中我们需要判断文本内容是否为空，感觉一个一个的判断特别费事而且影响效率，所以我用了GroupBOX，这样判断个人感觉比较省事：

UI层虚方法：

   下面是父窗体中定义的一些虚方法，需要子窗体具体的去实现：

<span style="font-family:SimSun;font-size:18px;">  '获得数据库中字段的名字
    Protected Overridable Function GetEnglish(cmbName As String) As String
        Return ""
    End Function
    '获得数据库中表名字
    '在这里给了我思路，既然可以把表名传过来
    '为什么不能把实体名传过来呢？so定义了一个GetEntity
    Protected Overridable Function GetTable() As String
        Return ""
    End Function
    '获得实体的名字
    Protected Overridable Function GetEntity() As Object
        Return ""
    End Function

    '定义DataGridView中用来显示的虚方法
    '这里需要做相应的改动，把从数据库中查到的消息作为参数传到相应的子窗体中
    Protected Overridable Sub Todgv(ByVal mylist As Object)

    End Sub</span>

相应的子窗体UI层：

<span style="font-family:SimSun;font-size:18px;"><pre name="code" class="vb"> '重载获得数据库中表的名字的方法
    Protected Overrides Function GetTable() As String
        Return "Worklogin"
    End Function
    '这是工作记录查询窗体，相应的把实体传给父窗体
    Protected Overrides Function GetEntity() As Object
        Return "Entity.OlineWorkerEntity"
    End Function
    '重载在datagridview中显示的方法
    Protected Overrides Sub Todgv(result As Object)
        '将参数作为数据源赋给datagridview
        Showall.DataSource = result
        Showall.Columns(0).Visible = False
        Showall.Columns(0).HeaderText = "工作人员"
        Showall.Columns(1).HeaderText = "级别"
        Showall.Columns(2).HeaderText = "上机日期"
        Showall.Columns(3).HeaderText = "上机时间"
        Showall.Columns(4).HeaderText = "下机日期"
        Showall.Columns(5).HeaderText = "下机时间"
        Showall.Columns(6).HeaderText = "工作电脑"
        Showall.Columns(7).HeaderText = "现在状态"
        Showall.DefaultCellStyle.Font = New Font("楷体", 16)
        Showall.AutoResizeColumns()
        Showall.ReadOnly = True’只读

    End Sub
</span>

Facade平淡无奇，所以就不写了，但是注意因为返回的类型不确定，所以定义为Object类型

重点的BLL层来了

    在这里判断实体类型，相对的通过Factory、IDAL，将其传到D层不同的方法中，之前我是吧判断放到D层的，但是感觉不太好，毕竟B层是业务逻辑判断嘛，D层还是本本分分的好了：

<span style="font-family:SimSun;font-size:18px;">  Public Function QueryAll(ByVal groupCheck As Entity.CHECKEntity) As Object
        '动态将entity送给mylist()

        Dim iQuery As IDAL.ICHECK
        Dim FctQ As New Factory.CHECKFactory
        iQuery = FctQ.SelectOnOff
        '学生账单
        If groupCheck.GetEntity = "Entity.StudentBillEntity" Then

            Dim mylist As List(Of Entity.StudentBillEntity)
            mylist = iQuery.IStudentBill(groupCheck)
            Return mylist

            '值班老师
        ElseIf groupCheck.GetEntity = "Entity.OlineWorkerEntity" Then
            Dim mylist As List(Of Entity.OnlineWorkerEntity)
            mylist = iQuery.IWorkerCord(groupCheck)
            Return mylist

            '学生信息
        ElseIf groupCheck.GetEntity = "Entity.RegisterEntity" Then
            Dim mylist As List(Of Entity.RegisterEntity)
            mylist = iQuery.IStudentSmg(groupCheck)
            Return mylist

        Else
            '上机记录
            Dim mylist As List(Of Entity.OnlineEntity)
            mylist = iQuery.IOnline(groupCheck)
            Return mylist

        End If


    End Function
</span>

Factory、IDAL层 低调  ~~~~~

D层：

     CheckQuery部分的代码是下面四个Function都要用到的，难得要敲四遍吗？不仅低效率而且浪费时间，(⊙﹏⊙)b果断放弃，把他单独提前了出来，用的时候调用好了

<span style="font-family:SimSun;font-size:18px;">  Public Function CheckQuery(groupcheck As Entity.CHECKEntity) As DataTable
        Dim sql As String
        sql = "select * from " & groupcheck.getTable & " where "
        '一个查询条件;
        '如果第一个组合条件为空则()
        If Trim(groupcheck.CmbCombination1) = "" Then
            sql = sql & groupcheck.CmbName1 & groupcheck.CmbRelation1 & "'" & groupcheck.TxtQuery1 & "'"
        Else
            '两个查询条件
            If Trim(groupcheck.CmbCombination2) = "" Then
                sql = sql & groupcheck.CmbName1 & groupcheck.CmbRelation1 & "'" & groupcheck.TxtQuery1 & "'" & groupcheck.CmbCombination1 & " " & groupcheck.CmbName2 & groupcheck.CmbRelation2 & "'" & groupcheck.TxtQuery2 & "'"
                '三个条件
            Else
                sql = sql & groupcheck.CmbName1 & groupcheck.CmbRelation1 & "'" & groupcheck.TxtQuery1 & "'" & groupcheck.CmbCombination1 & " " & groupcheck.CmbName2 & groupcheck.CmbRelation2 & "'" & groupcheck.TxtQuery2 & "'" & groupcheck.CmbCombination2 & " " & groupcheck.CmbName3 & groupcheck.CmbRelation3 & "'" & groupcheck.TxtQuery3 & "'"

            End If
        End If

        Dim dt As DataTable

        dt = LoginSqlHelper.GetDataTable(sql, CommandType.Text)
        Return dt
        If dt.Rows.Count = 0 Then
            Return Nothing
            Exit Function
        End If
    End Function
    '上机记录
    Public Function IOnline(groupcheck As CHECKEntity) As List(Of OnlineEntity) Implements IDAL.ICHECK.IOnline

        Dim QueryDt As DataTable = CheckQuery(groupcheck)
        Dim mylist As List(Of Entity.OnlineEntity)
        mylist = DataToList.convertToList(Of Entity.OnlineEntity)(QueryDt)
        Return mylist

    End Function
    '账单记录
    Public Function IStudentBill(groupcheck As CHECKEntity) As List(Of StudentBillEntity) Implements IDAL.ICHECK.IStudentBill

        Dim QueryDt As DataTable = CheckQuery(groupcheck)
        Dim mylist As List(Of Entity.StudentBillEntity)
        mylist = DataToList.convertToList(Of Entity.StudentBillEntity)(QueryDt)
        Return mylist

    End Function
    '学生信息
    Public Function IStudentSmg(groupcheck As CHECKEntity) As List(Of RegisterEntity) Implements IDAL.ICHECK.IStudentSmg

        Dim QueryDt As DataTable = CheckQuery(groupcheck)
        Dim mylist As List(Of Entity.RegisterEntity)
        mylist = DataToList.convertToList(Of Entity.RegisterEntity)(QueryDt)
        Return mylist

    End Function
    '工作记录
    Public Function IWorkerCord(groupcheck As CHECKEntity) As List(Of OnlineWorkerEntity) Implements IDAL.ICHECK.IWorkerCord

        Dim QueryDt As DataTable = CheckQuery(groupcheck)
        Dim mylist As List(Of Entity.OnlineWorkerEntity)
        mylist = DataToList.convertToList(Of Entity.OnlineWorkerEntity)(QueryDt)
        Return mylist

    End Function</span>

这样基本上组合查询就OK了：

     界面设计不怎么美观，那是因为秉承着实用的观点，其实是有点懒，嘘~~

    组合查询是一个很好的舞台，在UI层用哈希表实现加载Combobox的item既方便有不易出错是一个很好助手；単例模式大家也不防试一试，很不错的知识而且也可以让我们在实践中对他们有更进一步的了解，这里限于篇幅就不写了，机房重构、加油哦！！！

THANKS FOR YOUR TIME。